Thank you for the advice on the IDs, I will sort that out. I found a tut online which explained how to achieve what I did. Could you advise how to do it differently, or point me to a tutorial to explain it? I can see how show hide in Dreamweaver would do it, but I need the images to be in the same place, on top of each other as it were.

If you place the first image where you want it you can then use JavaScript to change the src of the IMG tag when the links are clicked instead of hiding and showing. I don't know if one method is more effective than the other, but it seems easier this way since it's only equally sized images involved.